This invention relates to an improved process for preparing polychlorobenzamide derivatives and more particularly pertains to a process for synthesizing said derivatives from corresponding polychlorobenzonitrile compound in near quantitative yields.
Polyhalobenzamide derivatives are well known compounds that are highly effective biocidal agents, e.g., fungicides, herbicides, bactericides, and the like. Furthermore, the derivatives are useful as progenitors of secondary and tertiary amides, (e.g. N-alkyl, N,N-dialkyl, N-aryl, N,N-diaryl) that are known biocidal agents. The compounds may also be used in flame-retardant resins, plasticizers, dyes, coatings and the like.
However, the utilization of polyhalobenzamide derivatives has been somewhat restricted in view of the limited production and expense of the compounds. Apparently this has been due to several factors, e.g., the relative inaccessability of suitable precursors and low yields of the derivatives prepared by prior art processes.
There are a few processes known in the art for the preparation or synthesis of certain polyhalobenzamide derivatives. For example, British Pat. No. 1,085,474 (1967) discloses a process for producing pentachlorobenzamide and four other derivatives by treating pentachlorobenzoyl chloride with appropriate co-reactants. However, the preparation of polyhalobenzamide derivatives by this process is disadvantageous in that polyhalobenzoyl chloride derivatives are not available in economical commercial quantities. Hence, the preparation of polyhalobenzamide derivatives in accordance with the teachings of this process would appear to be quite expensive, from a commercial standpoint.
Another prior art process is disclosed in U.S. Pat. No. 3,313,859 to Dorfman et al. (1967). Dorfman et al. teach a process for producing tetrahalohydroxybenzamides wherein a pentahalobenzamide is heated with a strong base dissolved in a solvent quantity of ethylene glycol or methanol. It is believed readily apparent that the process disclosed by Dorfman et al. has the disadvantage of starting with a polyhalobenzamide derivative as a precursor. As stated hereinbefore, polyhalobenzamide derivatives including pentahalobenzamides, prepared by prior art processes are quite expensive and are in relatively short supply, from a commercial standpoint.
On the other hand, processes for producing polyhalobenzonitrile derivatives in relatively economical commercial amounts have recently been developed. Commercial quantities of certain polyhalobenzonitrile derivatives, e.g., pentachlorobenzonitrile, are readily available.
There are classical methods known in the art to effect the conversion of nitrile derivatives to amide derivatives, for example, mixing and reacting a nitrile with hot caustic, hot alcoholic caustic, mixtures of phosphoric and acetic acids, and the like. However, experiments have shown that the classical methods fail to effect the conversion of polyhalobenzonitrile derivatives to corresponding polyhalobenzamide derivatives particularly in yields that are economically feasible, e.g., yields greater than 90%.
It has been previously reported that various aromatic nitriles are hydrolyzed to the corresponding acid by boiling the nitrile for several hours with 60 to 70% sulfuric acid. However, some aromatic nitriles in which substitution occurs in the two ortho positions have been shown to produce only the amide. Claus and Storenhagen (Ann. 1892, 269,228) report that 2:6 dichlorobenzonitrile is the notable exception being converted directly to the corresponding acid when heated at 150.degree. C.
It is well known that in hydrolyzing nitriles, an amide intermediate is formed; however, in most cases the amide is further hydrolyzed to the acid. For example, Sodbrough, Jackson and Lloyd, at page 232 disclose that 2:4:6-trichlorobenzamide is hydrolyzed at 160.degree. C. in the presence of excess 75% sulfuric acid to the corresponding acid with a 48.18 wt. % conversion.
Unexpectedly and contrary to the teachings of the prior art, it has now been discovered that a polychlorobenzonitrile compound having at least four chloro substituents can be directly converted to the corresponding polychlorobenzamide with essentially no further hydrolysis to the acid in accordance with the instant invention.